Agriculture workers actively seek ways to improve the economic output of commercial crops. For example, in cotton crops, workers seek to improve such growth factors as increased boll set, increased floral initiation, decreased floral abscissionincreased germination, decreased boll abscission, and enhanced root growth. Workers also seek to increase plant tolerance to environmental stress.
Formulations containing plant growth regulators (PGRs) have been developed to improve the economic yield of agricultural plants. Plant growth retardants and inhibitors of ethylene biosynthesis or action are two types of PGRs. Some plant growth retardants have been shown to inhibit gibberellin biosynthesis resulting in the reduction of shoot height in small grains and cotton. This reduction in shoot height has a strong economic benefit since it provides for less lodging in small grains and reduction of excessive vegetative growth. It also provides more uniform ripening in cotton.
Three groups of gibberellin biosynthesis inhibitors are known. The first group encompasses compounds with quaternary ammonium, phosphonium or sulphonium moieties. One example of a compound from this group is mepiquat chloride, described in U.S. Pat. No. 3,905,798 and incorporated herein by reference. Mepiquat chloride may increase cotton yields, boll load, lint yield and seed yield. Mepiquat chloride is also known to reduce vegetative growth, plant height and boll rot. Mepiquat chloride also induces uniform ripeness if the plants are treated early during their development. Chloromequat chloride is also a representative compound of this group.
The second group of plant growth retardants encompasses compounds with a nitrogen containing heterocycle such as flurprimidol, paclobutrazol, uniconazole and ancymidol.
The third group encompasses acylcylcohexanediones (such as trinexapac-ethyl and prohexadione-Ca) and daminozide.
It is known that ethylene is involved in plant senescence and plant stress reactions. Ethylene is also involved in leaf, flower, and fruit abscission. Hence, agents that inhibit or regulate the production of ethylene in plants or control its action have been developed in an effort to improve the yield of agricultural crops. Inhibitors of ethylene biosynthesis include substituted oxime-ethers as described in U.S. Pat. No. 4,744,811, incorporated herein by reference. These compounds are also described in PCT Application WO 95-02211, incorporated herein by reference, as being soil amendment compositions that increase the assimilation of nitrogen by higher plants.
Other inhibitors of ethylene biosynthesis and action include aminoethoxyvinylglycine ("AVG"), aminooxyacetic acid ("AOA"), rhizobitoxine, and methoxyvinyl glycine ("MVG"). Silver ions (e.g. silver thiosulfate), and 2,5-norbornadiene inhibit ethylene action.
Plant growth regulators have also been used to protect crops from the effects of environmental stress. Gianfagna, T. J. et al. "Mode of Action and Use of Growth Retardants in Reducing the Effects of Environmental Stress on Horticultural Crops: Karssen, C. N. et al. (eds.) Progress in Plant Growth Regulation, pp. 778-87 (1992). For example, researchers found that if ethephon was applied at a low rate (0.08 mM) it significantly delayed bloom in peach and reduced side effects. Researchers also found that ethephon increased the yields and hardiness of several horticultural plants.
Although PGRs have been developed as a means to improve agricultural crop yields, certain obstacles make the actual use of the PGR prohibitive. For example, many of the compounds display phytotoxicity. Other compounds are difficult to synthesize.
Many compounds require high rate applications to be effective. For example, PCT Application WO 93/07747, incorporated herein by reference, describes an improvement in a plant growth factor by applying aminoethoxyvinylglycine ("AVG"), an inhibitor of ethylene biosynthesis, to cotton plants. As the rate of AVG treatment increased, so did the improvement. (WO 93/07747, Examples 24). Assuming that a spray volume of 500 I/ha was used, the rates of application described in WO 93107747 would be approximately 62.5 to 500 g ai/ha (ai=active ingredient). The maximum rate response occurs at the highest rates.
High rate applications may result in a significant waste of material and may result in the discharge of the PGRs into the surrounding environment. Also, although many of these compounds may induce a beneficial growth habit, they do not provide consistent improvement in plant growth factors. Other compounds may lose their effectiveness or cause a reduction in yield when applied to species which are under some form of environmental stress.
Thus, it is an object of the invention to formulate a PGR that not only improves a plant growth factor but one that also reduces toxicity. It is also an object of the present invention to provide a PGR that has lower application rates and has limited environmental impact.